1. Field of the Invention
The present invention relates to a flashing device of an automatic light-regulation type.
2. Description of the Related Art
It is known that there is a camera having a built-in flashing device of an automatic light-regulation type. In this flashing device, the flash light reflected by a subject is received by a light receiving circuit to integrate a light amount. The light receiving circuit comprises a light receiving element. When an integral voltage corresponding to the integrated amount reaches a predetermined reference voltage, discharge of a main capacitor is intercepted in a flash discharge tube so that flashing is stopped. In this way, a flash-light amount is regulated so as to obtain a proper exposure amount.
In order to judge whether or not the integral voltage reaches the reference voltage, the reference voltage and the integral voltage are generally applied to a voltage comparator to compare these voltages in an analog amount. When the integral voltage reaches the reference voltage, an output signal from the voltage comparator is changed. For example, connection between the flash discharge tube and the main capacitor is intercepted by a semiconductor switching element to stop the flash light.
Meanwhile, the light receiving circuit is generally constituted of a light receiving element and a capacitor. The light receiving element is, for example, a photo transistor or a photo diode. The flash light reflected by a subject is received with the light receiving element. Then, the capacitor is charged by a photocurrent corresponding to an amount of the received light to integrate the light amount. A charging voltage of the capacitor is outputted as an integral voltage corresponding to the integrated amount.
By the way, as to the above-mentioned light receiving circuit, it is difficult to dissolve the dispersion of its photosensitivity. In other words, even if the light receiving circuit is constituted of the light receiving element and the capacitor which are of the same standard, and even if the same light amount is applied to the light receiving element, the dispersion of the outputted integral voltage is caused. The dispersion of the photosensitivity is especially drawn by dispersion of the light receiving element itself, for example a photo transistor. When the photosensitivity of the light receiving circuit has the dispersion, a light regulation level does not become constant. Hence, a proper exposure amount is not obtained. In view of this, the light regulation level is adjusted at the time of manufacturing the flashing device of the automatic light-regulation type.
As to methods for adjusting the light regulation level, there are some methods, in one of which, the reference voltage inputted into the voltage comparator is adjusted, and in another of which, the photosensitivity itself of the light receiving circuit is adjusted. In the former method, a variable resistor is provided in a circuit for generating the reference voltage. By changing a resistance value of the variable resistor, the reference voltage is increased or decreased so as to be adjusted in accordance with the photosensitivity of the light receiving circuit. Meanwhile, in the latter method, a filter having a proper density (transmittance) is disposed in front of the light receiving element. In another way, a circuit constant of the light receiving circuit, for example capacity of the capacitor is increased or decreased. Owing to this, a ratio of the outputted integral voltage to the incidence-light amount of the light receiving circuit, namely the photosensitivity is adjusted.
However, in the above-mentioned flashing device using the voltage comparator, many parts are required for automatically regulating the light. As the required parts, there are the voltage comparator, a circuit for generating the reference voltage, a circuit for adjusting the reference voltage, and so forth. Due to these parts, it is prevented to be downsized and to lower the manufacturing cost.
On the other hand, as to the flashing device in which the light regulation level is adjusted by adjusting the reference voltage with the variable resistor, it is necessary to manually adjusting the reference value of the variable resistor and to set the reference voltage to a certain voltage corresponding to the photosensitivity of the light receiving circuit. Thus, it takes a long operation time for adjustment so that operation efficiency becomes worse. Moreover, there is a limit to accuracy of the adjustment. Thus, it is difficult to perform the adjustment with great accuracy. Further, the variable resistor is comparatively expensive so that the manufacturing cost is prevented from being lowered.
As to the flashing devices in which the filter is arranged and the light regulation level is adjusted by changing the capacity of the capacitor of the light receiving circuit, the filter and the capacitor are manually exchanged and are manually added so that the adjustment can not be effectively performed. Moreover, there arise problems in that it is necessary to prepare various kinds of filters having the different densities, and in that it is necessary to prepare various kinds of capacitors having the different capacity.
In view of the foregoing, it is a primary object of the present invention to provide a flashing device in which parts of a circuit for automatically regulating the light may be reduced.
It is a second object of the present invention to provide a flashing device in which a light regulation level may be adjusted by simple structure and by using low-priced parts.
In order to achieve the above and other objects, the flashing device according to the present invention repeatedly performs flashing in a pulse state. At this time, the flash light reflected by a subject is received by a light receiving element. Based on a photocurrent flowing from the light receiving element, the received light amount is integrated. When the integrated amount reaches a value corresponding to a predetermined level, succeeding flashing is stopped. Thus, the flash-light amount may be controlled with accuracy.
Moreover, a capacitor is charged by the photocurrent flowing the light receiving element to integrate the light amount. A charging voltage of the capacitor is sampled by an A-D converter as an integral voltage. Integral voltage data obtained from the A-D converter is compared with a predetermined reference voltage data. When the integral voltage data is equal to the reference voltage data or more, flashing is stopped. Owing to this structure, a number of parts may be reduced.
Further, the photocurrent flowing from the light receiving element is converted to a light-reception voltage while flashing is performed in the pulse state. The converted one is sampled by the A-D converter. Based on light-reception voltage data obtained from the A-D converter, the flash light is integrated. Integral voltage data corresponding to the integrated amount is compared with a predetermined reference voltage data. When the integral voltage data is equal to the reference voltage data or more, flashing is stopped. Owing to this structure, a number of parts may be reduced.
In the flashing device according to another embodiment, the flash light reflected by a subject is integrated by a light receiving circuit constituted of a light receiving element and a capacitor. In this flashing device, a semiconductor switching element is connected to the light receiving element in series and is turned on and off in a certain cycle. A ratio of an on-period of the switching element to the cycle thereof is varied. By varying this ratio, photosensitivity of the light receiving circuit may be easily adjusted, using low-priced parts. Thus, a light regulation level may be adjusted so as to obtain a predetermined flash-light amount.
In the flashing device according to other embodiment, the light amount is integrated based on a photocurrent flowing from a light receiving element. A voltage corresponding to an inputted voltage-control signal is applied to the light receiving element. By changing the voltage applied to the light receiving element, photosensitivity of the light receiving circuit is easily adjusted. Thus, the light regulation level may be adjusted so as to obtain a predetermined flash-light amount.